Bagheera (3.5e NPC)

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The rules state that a creature of the animal type has an Int score of 1 or 2 and that no creature with an Int score of 3 or higher can be an animal, and should an animal increase its Int to 3+ it becomes a magical beast instead.

So how does this affect animal companions? Well, normally an animal companion can only be of the animal type. So if something were to happen to change an existing companion's type, one might conclude that the former animal would be granted immediate dismissal, whether the controlling character desired it or not.

Continuing on this line of thought, the former animal loses all the benefits of being an animal companion, but now has human-like sentience and free will. It's under the DM's control at this point, and will most likely take action based on its instincts and/or how the controlling character treated it during its term as an animal companion.

Bagheera was once a companion to a halfling ranger who, at times, could be quite abusive to him. In fact, Bagheera seemed nothing more than a tool for the ranger's whimsical use and abuse.

At one point, the halfling—thinking he could teach Bagheera more tricks if he were a little smarter, and thus be a little more useful—the halfling puts a headband of intellect on Bagheera.

As the ranger anticipated, Bagheera became smarter. What didn't expect was that headband somehow broke the bond between ranger and animal companion, and both simultaneously sensed the severing and knew that the other felt it, too.

Feeling a bit confused about the influx of intelligence and more than a little resentful of the ranger's abuse, Bagheera bolted when the ranger reached toward him to retrieve the headband. In an effort to get it back (and Bagheera suspected there were other reasons, as well), the halfling hounded Bagheera night and day.

The halfling's persistence angered Bagheera more than anything else. He wanted nothing more to do with him, and just wanted to be left alone. Second to that, he wanted to see his pursuer dead. One thing that stopped him from doing just that was that he remembered his prowess as a warrior, and knew that he might not win such a confrontation. The stubbornness of the halfing's pursuit, started to wear thin on Bagheera, because they both know that the halfling will eventually catch up to the feline. Paranoia began to eat away at Bagheera's mind.

During one particularly dogged segment of the hunt, Bagheera had the halfling close on his heels, and stumbled into a halfling village. In his desperate state of mind, when Bagheera saw the villagers, he thought himself surrounded by more of what was hounding him, and was angered that they wouldn't leave him alone. He took his aggressions out on the villagers, and when the halfling chasing him saw the scene, he stood in shock of the carnage.

Bagheera took advantage of the halfling's stunned state, and put an end to the chase once and for all.

He now makes his home in mountainous terrain, and attacks any halflings on sight. He has progressed to the point that even the headband were removed he'd still be more than just a dumb animal.